- Volume 151, Issue 1, 2005
Volume 151, Issue 1, 2005
- Microbiology Comment
-
- Biochemistry And Molecular Biology
-
-
-
Respiratory gene clusters of Metallosphaera sedula – differential expression and transcriptional organization
More LessMetallosphaera sedula is a thermoacidophilic Crenarchaeon which is capable of leaching metals from sulfidic ores. The authors have investigated the presence and expression of genes encoding respiratory complexes in this organism when grown heterotrophically or chemolithotrophically on either sulfur or pyrite. The presence of three gene clusters, encoding two terminal oxidase complexes, the quinol oxidase SoxABCD and the SoxM oxidase supercomplex, and a gene cluster encoding a high-potential cytochrome b and components of a bc 1 complex analogue (cbsBA–soxL2N gene cluster) was established. Expression studies showed that the soxM gene was expressed to high levels during heterotrophic growth of M. sedula on yeast extract, while the soxABCD mRNA was most abundant in cells grown on sulfur. Reduced-minus-oxidized difference spectra of cell membranes showed cytochrome-related peaks that correspond to published spectra of Sulfolobus-type terminal oxidase complexes. In pyrite-grown cells, expression levels of the two monitored oxidase gene clusters were reduced by a factor of 10–12 relative to maximal expression levels, although spectra of membranes clearly contained oxidase-associated haems, suggesting the presence of additional gene clusters encoding terminal oxidases in M. sedula. Pyrite- and sulfur-grown cells contained high levels of the cbsA transcript, which encodes a membrane-bound cytochrome b with a possible role in iron oxidation or chemolithotrophy. The cbsA gene is not co-transcribed with the soxL2N genes, and therefore does not appear to be an integral part of this bc 1 complex analogue. The data show for the first time the differential expression of the Sulfolobus-type terminal oxidase gene clusters in a Crenarchaeon in response to changing growth modes.
-
-
-
-
Disruption of MRG19 results in altered nitrogen metabolic status and defective pseudohyphal development in Saccharomyces cerevisiae
More LessIt was previously shown that MRG19 downregulates carbon metabolism in Saccharomyces cerevisiae upon glucose exhaustion, and that the gene is glucose repressed. Here, it is shown that glucose repression of MRG19 is overcome upon nitrogen withdrawal, suggesting that MRG19 is a regulator of carbon and nitrogen metabolism. β-Galactosidase activity fostered by the promoter of GDH1/3, which encode anabolic enzymes of nitrogen metabolism, was altered in an MRG19 disruptant. As compared to the wild-type strain, the MRG19 disruptant showed a decrease in the ratio of 2-oxoglutarate to glutamate under nitrogen-limited conditions. MRG19 disruptants showed reduced pseudohyphal formation and enhanced sporulation, a phenomenon that occurs under conditions of both nitrogen and carbon withdrawal. These studies revealed that MRG19 regulates carbon and nitrogen metabolism, as well as morphogenetic changes, suggesting that MRG19 is a component of the link between the metabolic status of the cell and the corresponding developmental pathway.
-
-
-
Acetaminophen toxicity and resistance in the yeast Saccharomyces cerevisiae
More LessAcetaminophen (paracetamol), one of the most widely used analgesics, is toxic under conditions of overdose or in certain disease conditions, but the mechanism of acetaminophen toxicity is still not entirely understood. To obtain fresh insights into acetaminophen toxicity, this phenomenon was investigated in yeast. Acetaminophen was found to be toxic to yeast cells, with erg mutants displaying hypersensitivity. Yeast cells grown in the presence of acetaminophen were found to accumulate intracellular acetaminophen, but no metabolic products of acetaminophen could be detected in these extracts. The toxicity response did not lead to an oxidative stress response, although it did involve Yap1p. The cytochrome P450 enzymes of yeast, Erg5p and Erg11p, did not appear to participate in this process, unlike the mammalian systems. Furthermore, we could not establish a central role for glutathione depletion or the cellular glutathione redox status in acetaminophen toxicity, suggesting differences from mammalian systems in the pathways causing toxicity. Investigations of the resistance mechanisms revealed that deletion of the glutathione-conjugate pumps Ycf1p (a target of Yap1p) and Bpt1p, surprisingly, led to acetaminophen resistance, while overexpression of the multidrug resistance pumps Snq2p and Flr1p (also targets of Yap1p) led to acetaminophen resistance. The Yap1p-dependent resistance to acetaminophen required a functional Pdr1p or Pdr3p protein, but not a functional Yrr1p. In contrast, resistance mediated by Pdr1p/Pdr3p did not require a functional Yap1p, and revealed a distinct hierarchy in the resistance to acetaminophen.
-
-
-
Temperature adaptation in Dictyostelium: role of Δ5 fatty acid desaturase
More LessMembrane fluidity is critical for proper membrane function and is regulated in part by the proportion of unsaturated fatty acids present in membrane lipids. The proportion of these lipids in turn varies with temperature and may contribute to temperature adaptation in poikilothermic organisms. The fundamental question posed in this study was whether the unsaturation of fatty acids contributes to the ability to adapt to temperature stress in Dictyostelium. First, fatty acid composition was analysed and it was observed that the relative proportions of dienoic acids changed with temperature. To investigate the role of dienoic fatty acids in temperature adaptation, null mutants were created in the two known Δ5 fatty acid desaturases (FadA and FadB) that are responsible for the production of dienoic fatty acids. The fadB null mutant showed no significant alteration in fatty acid composition or in phenotype. However, the disruption of fadA resulted in a large drop in dienoic fatty acid content from 51·2 to 4·1 % and a possibly compensatory increase in monoenoic fatty acids (40·9–92·4 %). No difference was detected in temperature adaptation with that of wild-type cells during the growth phase. However, surprisingly, mutant cells developed more efficiently than the wild-type at elevated temperatures. These results show that the fatty acid composition of Dictyostelium changes with temperature and suggest that the regulation of dienoic fatty acid synthesis is involved in the development of Dictyostelium at elevated temperatures, but not during the growth phase.
-
-
-
A unique nine-gene comY operon in Streptococcus mutans
More LessMany Gram-positive and Gram-negative bacteria possess natural competence mechanisms for DNA capture and internalization. In Bacillus subtilis, natural competence is absolutely dependent upon the presence of a seven-gene operon known as the comG operon (comGA–G). In species of Streptococcus, this function has been described for a four-gene operon (comYA–D in Streptococcus gordonii and cglA–D in Streptococcus pneumoniae). In this study, a nine-orf operon (named comYA–I) required for natural competence in Streptococcus mutans was identified and characterized. Orf analysis of this operon indicates that the first four Orfs (ComYA–D) share strong homology with ComYA–D of S. gordonii and CglA–D of S. pneumoniae, the fifth to seventh Orfs (ComYE–G) match conserved hypothetical proteins from various species of Streptococcus with ComYF possessing a predicted ComGF domain, the eighth Orf (ComYH) shows a strong homology to numerous DNA methyltransferases from restriction/modification systems, and the ninth Orf (ComYI) is homologous to acetate kinase (AckA). RT-PCR analysis of the orf junctions confirmed that all nine orfs were present in a single transcript, while real-time RT-PCR analysis demonstrated that these orfs were expressed at a level very similar to that of the first orf in the operon. Mutations were constructed in all nine putative orfs. The first seven genes (comYA–G) were found to be essential for natural competence, while comYH and comYI had reduced and normal natural competence ability, respectively. Analyses of S. mutans comY–luciferase reporter fusions indicated that comY expression is growth-phase dependent, with maximal expression at an OD600 of about 0·2, while mutations in ciaH, comC and luxS reduced the level of comY expression. In addition, comY operon expression appears to be correlated with natural competence ability.
-
-
-
Characterization of the cleavage site and function of resulting cleavage fragments after limited proteolysis of Clostridium difficile toxin B (TcdB) by host cells
Clostridium difficile toxin B (TcdB) is a single-stranded protein consisting of a C-terminal domain responsible for binding to the host cell membrane, a middle part involved in internalization, and the N-terminal catalytic (toxic) part. This study shows that TcdB is processed by a single proteolytic step which cleaves TcdB10463 between Leu543 and Gly544 and the naturally occurring variant TcdB8864 between Leu544 and Gly545. The cleavage occurs at neutral pH and is catalysed by a pepstatin-sensitive protease localized in the cytoplasm and on the cytoplasmic face of intracellular membranes. The smaller N-terminal cleavage products [63 121 Da (TcdB10463) and 62 761 Da (TcdB8864)] harbour the cytotoxic and glucosyltransferase activities of the toxins. When microinjected into cultured Chinese hamster lung fibroblasts, the N-terminal cleavage fragment shows full cytotoxic activity shortly after injection whereas the holotoxin initially exhibits a very low activity which, however, increases with time. Twenty minutes after the start of internalization of TcdB, the larger cleavage products [206 609 Da (TcdB10463) and 206 245 Da (TcdB8864)] are found exclusively in a membrane fraction, whereas the N-terminal cleavage products appear mainly in the cytosol and associated with the membrane. This is in line with a proposed model according to which the longer, C-terminal, part of these toxins forms a channel allowing for the translocation of the toxic N-terminal part, which is subsequently cleaved off at the cytoplasmic face of an intracellular compartment, most likely endosomes.
-
-
-
The formation of cyclopropane fatty acids in Salmonella enterica serovar Typhimurium
More LessThe formation of cyclopropane fatty acid (CFA) and its role in the acid shock response in Salmonella enterica serovar Typhimurium (S. typhimurium) was investigated. Data obtained by GC/MS demonstrated that the CFA level in S. typhimurium increased upon its entry to the stationary phase, as in other bacteria. The cfa gene encoding CFA synthase was cloned, and mutants of the cfa gene were constructed by allelic exchange. A cfa mutant could not produce CFA and was sensitive to low pH. Introduction of a functional cfa gene into a cfa mutant cell made the mutant convert all unsaturated fatty acids to CFAs and partially restored resistance to low pH. Interestingly, the alternative sigma factor RpoS, which was induced during the stationary phase, affected the production of C19 CFA but not C17 CFA. Western blotting analysis showed that the increase in expression of CFA synthase at early stationary phase was due to the alternative sigma factor RpoS.
-
-
-
Detailed studies of the binding mechanism of the Sinorhizobium meliloti transcriptional activator ExpG to DNA
More LessThe exopolysaccharide galactoglucan promotes the establishment of symbiosis between the nitrogen-fixing Gram-negative soil bacterium Sinorhizobium meliloti 2011 and its host plant alfalfa. The transcriptional regulator ExpG activates expression of galactoglucan biosynthesis genes by direct binding to the expA1, expG/expD1 and expE1 promoter regions. ExpG is a member of the MarR family of regulatory proteins. Analysis of target sequences of an ExpG(His)6 fusion protein in the exp promoter regions resulted in the identification of a binding site composed of a conserved palindromic region and two associated sequence motifs. Association and dissociation kinetics of the specific binding of ExpG(His)6 to this binding site were characterized by standard biochemical methods and by single-molecule spectroscopy based on the atomic force microscope (AFM). Dynamic force spectroscopy indicated a distinct difference in the kinetics between the wild-type binding sequence and two mutated binding sites, leading to a closer understanding of the ExpG–DNA interaction.
-
-
-
DNA-binding activity of LndI protein and temporal expression of the gene that upregulates landomycin E production in Streptomyces globisporus 1912
The gene lndI is involved in the pathway-specific positive regulation of biosynthesis of the antitumour polyketide landomycin E in Streptomyces globisporus 1912. LndI was overexpressed in Escherichia coli as a protein C-terminally fused to the intein-chitin-binding-domain tag and purified in a one-step column procedure. Results of in vivo LndI titration, DNA gel mobility-shift assays and promoter-probing experiments indicate that LndI is an autoregulatory DNA-binding protein that binds to its own gene promoter and to the promoter of the structural gene lndE. Enhanced green fluorescent protein was used as a reporter to study the temporal and spatial pattern of lndI transcription. Expression of lndI started before cells entered mid-exponential phase and peak expression coincided with maximal accumulation of landomycin E and biomass. In solid-phase analysis, lndI expression was evident in substrate mycelia but was absent from aerial hyphae and spores.
-
- Biodiversity And Evolution
-
-
-
Molecular evolution of Vibrio pathogenicity island-2 (VPI-2): mosaic structure among Vibrio cholerae and Vibrio mimicus natural isolates
More LessVibrio cholerae is a Gram-negative rod that inhabits the aquatic environment and is the aetiological agent of cholera, a disease that is endemic in much of Southern Asia. The 57·3 kb Vibrio pathogenicity island-2 (VPI-2) is confined predominantly to toxigenic V. cholerae O1 and O139 serogroup isolates and encodes 52 ORFs (VC1758 to VC1809), which include homologues of an integrase (VC1758), a restriction modification system, a sialic acid metabolism gene cluster (VC1773–VC1783), a neuraminidase (VC1784) and a gene cluster that shows homology to Mu phage. In this study, a 14·1 kb region of VPI-2 comprising ORFs VC1773 to VC1787 was identified by PCR and Southern blot analyses in all 17 Vibrio mimicus isolates examined. The VPI-2 region in V. mimicus was inserted adjacent to a serine tRNA similar to VPI-2 in V. cholerae. In 11 of the 17 V. mimicus isolates examined, an additional 5·3 kb region encoding VC1758 and VC1804 to VC1809 was present adjacent to VC1787. The evolutionary history of VPI-2 was reconstructed by comparative analysis of the nanH (VC1784) gene tree with the species gene tree, deduced from the housekeeping gene malate dehydrogenase (mdh), among V. cholerae and V. mimicus isolates. Both gene trees showed an overall congruence; on both gene trees V. cholerae O1 and O139 serogroup isolates clustered together, whereas non-O1/non-O139 serogroup isolates formed separate divergent branches with similar clustering of strains within the branches. One exception was noted: on the mdh gene tree, V. mimicus sequences formed a distinct divergent lineage from V. cholerae sequences; however, on the nanH gene tree, V. mimicus clustered with V. cholerae non-O1/non-O139 isolates, suggesting horizontal transfer of this region between these species.
-
-
- Environmental Microbiology
-
-
-
Degradation of the xenoestrogen nonylphenol by aquatic fungi and their laccases
More LessDegradation of technical nonylphenol (t-NP), known as an endocrine-disrupting compound mixture, was assessed, using the mitosporic fungal strain UHH 1-6-18-4 isolated from nonylphenol-contaminated river water, and a strain of the aquatic hyphomycete Clavariopsis aquatica. GC-MS analysis could resolve 12 peaks attributable to nonyl chain-branched t-NP isomers. All were degraded, to individual extents. Analysis of degradation metabolites suggested intracellular hydroxylation of the nonyl moieties of individual t-NP isomers. Further metabolites also indicated shortening of branched nonyl chains, and 4-hydroxybenzoic acid was identified as a t-NP breakdown product in UHH 1-6-18-4. The t-NP degradation efficiency was higher in UHH 1-6-18-4 than in C. aquatica, and a lower specificity in degradation of individual t-NP constituents in UHH 1-6-18-4 than in C. aquatica was observed. Strain UHH 1-6-18-4 concomitantly produced extracellular laccase under degradation conditions. A mixture of CuSO4 and vanillic acid considerably enhanced laccase production in both fungi. Laccase preparations derived from UHH 1-6-18-4 and C. aquatica cultures also converted t-NP. Laccase-catalysed transformation of t-NP led to the formation of products with higher molecular masses than that of the parent compound. These results emphasize a role of fungi occurring in aquatic ecosystems in degradation of water contaminants with endocrine activity, which has not previously been considered. Furthermore, the results are in support of two different mechanisms employed by fungi isolated from aquatic environments to initiate t-NP degradation: hydroxylation of individual t-NP isomers at their branched nonyl chains and further breakdown of the alkyl chains of certain isomers; and attack of t-NP by extracellular laccase, the latter leading to oxidative coupling of primary radical products to compounds with higher molecular masses.
-
-
-
-
Different gvpC length variants are transcribed within single filaments of the cyanobacterium Planktothrix rubescens
More LessTranscripts of the gas vesicle genes gvpA and gvpC were detected in single filaments of the cyanobacterium Planktothrix rubescens using reverse transcription and quantitative real-time PCR. Primers were designed to amplify short sequences within gvpA and three length variants of gvpC. With genomic template DNA, and using Sybr Green to monitor product accumulation, similar amplification efficiencies were observed for each of these genes. The relative copy numbers of gvpC length variants in genomic DNA from five Planktothrix gas vesicle genotypes determined by real-time PCR were similar to those indicated by sequencing the gas vesicle gene clusters. The precipitation of gvp cDNA reverse-transcribed from cellular RNA from single filaments was required before amplification of the gene fragments; without this step it was not possible to detect the accumulation of the expected amplicons by dissociation analysis. Precipitation was also necessary to ensure the generation of product curves that allowed linear regression in an early stage of PCR, a prerequisite for the quantification of low-input cDNA amounts without the need for standard curves. This report shows that different gvpC length variants are transcribed within single Planktothrix filaments, both from laboratory cultures and from natural samples taken from Lake Zürich. This has implications for the efficiency of buoyancy provision by the possible production of gas vesicles of different strengths within individual cyanobacterial filaments. The hypothesis that post-transcriptional regulation may influence the type of protein (GvpC) present in gas vesicles is presented.
-
-
-
Can genetically modified Escherichia coli with neutral buoyancy induced by gas vesicles be used as an alternative method to clinorotation for microgravity studies?
More LessSpace flight has been shown to affect various bacterial growth parameters. It is proposed that weightlessness allows the cells to remain evenly distributed, consequently altering the chemical makeup of their surrounding fluid, and hence indirectly affecting their physiological behaviour. In support of this argument, ground-based studies using clinostats to partially simulate the quiescent environment attained in microgravity have generally been successful in producing bacterial growth characteristics that mimic responses reported under actual space conditions. A novel approach for evaluating the effects of reduced cell sedimentation is presented here through use of Escherichia coli cultures genetically modified to be neutrally buoyant. Since clinorotation would not (or would only minimally) affect cell distribution of this already near-colloidal cell system, it was hypothesized that the effects on final population density would be eliminated relative to a static control. Gas-vesicle-producing E. coli cultures were grown under clinostat and static conditions and the culture densities at 60 h were compared. As a control, E. coli that do not produce gas vesicles, but were otherwise identical to the experimental strain, were also grown under clinostat and static conditions. As hypothesized, no significant difference was observed in cell populations at 60 h between the clinorotated and static gas-vesicle-producing E. coli cultures, while the cells that did not produce gas vesicles showed a mean increase in population density of 10·5 % (P=0·001). These results further suggest that the lack of cumulative cell sedimentation is the dominant effect of space flight on non-stirred, in vitro E. coli cultures.
-
-
-
Recovery of an environmental chlamydia strain from activated sludge by co-cultivation with Acanthamoeba sp.
Chlamydiae are a unique group of obligate intracellular bacteria comprising important pathogens of vertebrates as well as symbionts of free-living amoebae. Although there is ample molecular evidence for a huge diversity and wide distribution of chlamydiae in nature, environmental chlamydiae are currently represented by only few isolates. This paper reports the recovery of a novel environmental chlamydia strain from activated sludge by co-cultivation with Acanthamoeba sp. The recovered environmental chlamydia strain UV-7 showed the characteristic morphology of chlamydial developmental stages as revealed by electron microscopy and was identified as a new member of the family Parachlamydiaceae (98·7 % 16S rRNA sequence similarity to Parachlamydia acanthamoebae). Infection studies suggested that Parachlamydia sp. UV-7 is not confined to amoeba hosts but is also able to invade mammalian cells. These findings outline a new straightforward approach to retrieving environmental chlamydiae from nature without prior, tedious isolation and cultivation of their natural host cells, and lend further support to suggested implications of environmental chlamydiae for public health.
-
- Genes And Genomes
-
-
-
Gene expression diversity among Mycobacterium tuberculosis clinical isolates
More LessIntraspecies genetic diversity has been demonstrated to be important in the pathogenesis and epidemiology of several pathogens, such as HIV, influenza, Helicobacter and Salmonella. It is also important to consider strain-to-strain variation when identifying drug targets and vaccine antigens and developing tools for molecular diagnostics. Here, the authors present a description of the variability in gene expression patterns among ten clinical isolates of Mycobacterium tuberculosis, plus the laboratory strains H37Rv and H37Ra, growing in liquid culture. They identified 527 genes (15 % of those tested) that are variably expressed among the isolates studied. The remaining genes were divided into three categories based on their expression levels: unexpressed (38 %), low to undetectable expression (31 %) and consistently expressed (16 %). The expression categories were compared with functional categories and three biologically interesting gene lists: genes that are deleted among clinical isolates, T-cell antigens and essential genes. There were significant associations between expression variability and the classification of genes as T-cell antigens, involved in lipid metabolism, PE/PPE, insertion sequences and phages, and deleted among clinical isolates. This survey of mRNA expression among clinical isolates of M. tuberculosis demonstrates that genes with important functions can vary in their expression levels between strains grown under identical conditions.
-
-
-
-
In vivo analyses of constitutive and regulated promoters in halophilic archaea
More LessThe two gvpA promoters PcA and PpA of Halobacterium salinarum, and the PmcA promoter of Haloferax mediterranei were investigated with respect to growth-phase-dependent expression and regulation in Haloferax volcanii transformants using the bgaH reading frame encoding BgaH, an enzyme with β-galactosidase activity, as reporter. For comparison, the Pfdx promoter of the ferredoxin gene of Hbt. salinarum and the PbgaH promoter of Haloferax lucentense (formerly Haloferax alicantei) were analysed. Pfdx , driving the expression of a house-keeping gene, was highly active during the exponential growth phase, whereas PbgaH and the three gvpA promoters yielded the largest activities during the stationary growth phase. Compared to Pfdx , the basal promoter activities of PpA and PmcA were rather low, and larger activities were only detected in the presence of the endogenous transcriptional activator protein GvpE. The PcA promoter does not yield a detectable basal promoter activity and is only active in the presence of the homologous cGvpE. To investigate whether the PcA -TATA box and the BRE element were the reason for the lack of the basal PcA activity, these elements and also sequences further upstream were substituted with the respective sequences of the stronger PpA promoter and investigated in Hfx. volcanii transformants. All these promoter chimera did not yield a detectable basal promoter activity. However, whenever the PpA -BRE element was substituted for the PcA -BRE, an enhanced cGvpE-mediated activation was observed. The promoter chimeras harbouring PpA -BRE plus 5 (or more) bp further upstream also gained activation by the heterologous pGvpE and mcGvpE proteins. The sequence required for the GvpE-mediated activation was determined by a 4 bp scanning mutagenesis with the 45 bp region upstream of PmcA -BRE. None of these alterations influenced the basal promoter activity, but the sequence TGAAACGG-n4-TGAACCAA was important for the GvpE-mediated activation of PmcA .
-
-
-
Molecular analysis of the anaerobic rumen fungus Orpinomyces – insights into an AT-rich genome
More LessThe anaerobic gut fungi occupy a unique niche in the intestinal tract of large herbivorous animals and are thought to act as primary colonizers of plant material during digestion. They are the only known obligately anaerobic fungi but molecular analysis of this group has been hampered by difficulties in their culture and manipulation, and by their extremely high A+T nucleotide content. This study begins to answer some of the fundamental questions about the structure and organization of the anaerobic gut fungal genome. Directed plasmid libraries using genomic DNA digested with highly or moderately rich AT-specific restriction enzymes (VspI and EcoRI) were prepared from a polycentric Orpinomyces isolate. Clones were sequenced from these libraries and the breadth of genomic inserts, both genic and intergenic, was characterized. Genes encoding numerous functions not previously characterized for these fungi were identified, including cytoskeletal, secretory pathway and transporter genes. A peptidase gene with no introns and having sequence similarity to a gene encoding a bacterial peptidase was also identified, extending the range of metabolic enzymes resulting from apparent trans-kingdom transfer from bacteria to fungi, as previously characterized largely for genes encoding plant-degrading enzymes. This paper presents the first thorough analysis of the genic, intergenic and rDNA regions of a variety of genomic segments from an anaerobic gut fungus and provides observations on rules governing intron boundaries, the codon biases observed with different types of genes, and the sequence of only the second anaerobic gut fungal promoter reported. Large numbers of retrotransposon sequences of different types were found and the authors speculate on the possible consequences of any such transposon activity in the genome. The coding sequences identified included several orphan gene sequences, including one with regions strongly suggestive of structural proteins such as collagens and lampirin. This gene was present as a single copy in Orpinomyces, was expressed during vegetative growth and was also detected in genomes from another gut fungal genus, Neocallimastix.
-
-
-
Aminopeptidases and dipeptidyl-peptidases secreted by the dermatophyte Trichophyton rubrum
The nature of secreted aminopeptidases in Trichophyton rubrum was investigated by using a reverse genetic approach. T. rubrum genomic and cDNA libraries were screened with Aspergillus spp. and Saccharomyces cerevisiae aminopeptidase genes as the probes. Two leucine aminopeptidases, ruLap1 and ruLap2, and two dipeptidyl-peptidases, ruDppIV and ruDppV, were characterized and compared to orthologues secreted by Aspergillus fumigatus using a recombinant protein from Pichia pastoris. RuLap1 is a 33 kDa nonglycosylated protein, while ruLap2 is a 58–65 kDa glycoprotein. The hydrolytic activity of ruLap1, ruLap2 and A. fumigatus orthologues showed various preferences for different aminoacyl-7-amido-4-methylcoumarin substrates, and various sensitivities to inhibitors and cations. ruDppIV and ruDppV showed similar activities to A. fumigatus orthologues. In addition to endopeptidases, the four aminopeptidases ruLap1, ruLap2, ruDppIV and ruDppV were produced by T. rubrum in a medium containing keratin as the sole nitrogen source. Synergism between endo- and exopeptidases is likely to be essential for dermatophyte virulence, since these fungi grow only in keratinized tissues.
-
- Pathogens And Pathogenicity
-
-
-
Influence of the age and sex of human hosts on the distribution of Escherichia coli ECOR groups and virulence traits
More LessEscherichia coli were isolated from the faeces of 266 individuals living in the Canberra region of Australia. The isolates were characterized for their ECOR group membership (A, B1, B2 or D) and for the presence of 29 virulence-associated traits. Overall, 19·5 % of the strains were members of group A, 12·4 % B1, 45·1 % B2 and 22·9 % D. The frequency with which strains belonging to the four ECOR groups were observed varied with the age and sex of the hosts from which they were isolated. In males, the probability of isolating A or D strains increased with host age, whilst the probability of detecting a group B2 strain declined. In females, the probability of recovering A or B2 strains increased with increasing host age and there was a concomitant decline in the likelihood of isolating B1 or D strains. Of the 29 virulence-associated traits examined, 24 were detected in more than one strain. The likelihood of detecting most traits varied with a strain's ECOR membership, with the exception of afa/draBC, astA, cvaC, eaeA, iss and iutA, for which there was no statistically significant evidence of an association with ECOR group. The frequency with which fimH, iha, eaeA, iroN, hlyD, iss, ompT and K1 were detected in a strain depended on the age or sex of the host from which the strain was isolated. In group B2 strains many of the virulence traits were non-randomly associated, with some co-occurring in a strain less often than expected by chance, whilst others were co-associated. In 17 cases, the extent to which two virulence traits were co-associated was found to depend on host sex and age. The results of this study suggest that the morphological, physiological and dietary differences that occur among human individuals of different sex or age may influence the distribution of E. coli genotypes.
-
-
Volumes and issues
-
Volume 170 (2024)
-
Volume 169 (2023)
-
Volume 168 (2022)
-
Volume 167 (2021)
-
Volume 166 (2020)
-
Volume 165 (2019)
-
Volume 164 (2018)
-
Volume 163 (2017)
-
Volume 162 (2016)
-
Volume 161 (2015)
-
Volume 160 (2014)
-
Volume 159 (2013)
-
Volume 158 (2012)
-
Volume 157 (2011)
-
Volume 156 (2010)
-
Volume 155 (2009)
-
Volume 154 (2008)
-
Volume 153 (2007)
-
Volume 152 (2006)
-
Volume 151 (2005)
-
Volume 150 (2004)
-
Volume 149 (2003)
-
Volume 148 (2002)
-
Volume 147 (2001)
-
Volume 146 (2000)
-
Volume 145 (1999)
-
Volume 144 (1998)
-
Volume 143 (1997)
-
Volume 142 (1996)
-
Volume 141 (1995)
-
Volume 140 (1994)
-
Volume 139 (1993)
-
Volume 138 (1992)
-
Volume 137 (1991)
-
Volume 136 (1990)
-
Volume 135 (1989)
-
Volume 134 (1988)
-
Volume 133 (1987)
-
Volume 132 (1986)
-
Volume 131 (1985)
-
Volume 130 (1984)
-
Volume 129 (1983)
-
Volume 128 (1982)
-
Volume 127 (1981)
-
Volume 126 (1981)
-
Volume 125 (1981)
-
Volume 124 (1981)
-
Volume 123 (1981)
-
Volume 122 (1981)
-
Volume 121 (1980)
-
Volume 120 (1980)
-
Volume 119 (1980)
-
Volume 118 (1980)
-
Volume 117 (1980)
-
Volume 116 (1980)
-
Volume 115 (1979)
-
Volume 114 (1979)
-
Volume 113 (1979)
-
Volume 112 (1979)
-
Volume 111 (1979)
-
Volume 110 (1979)
-
Volume 109 (1978)
-
Volume 108 (1978)
-
Volume 107 (1978)
-
Volume 106 (1978)
-
Volume 105 (1978)
-
Volume 104 (1978)
-
Volume 103 (1977)
-
Volume 102 (1977)
-
Volume 101 (1977)
-
Volume 100 (1977)
-
Volume 99 (1977)
-
Volume 98 (1977)
-
Volume 97 (1976)
-
Volume 96 (1976)
-
Volume 95 (1976)
-
Volume 94 (1976)
-
Volume 93 (1976)
-
Volume 92 (1976)
-
Volume 91 (1975)
-
Volume 90 (1975)
-
Volume 89 (1975)
-
Volume 88 (1975)
-
Volume 87 (1975)
-
Volume 86 (1975)
-
Volume 85 (1974)
-
Volume 84 (1974)
-
Volume 83 (1974)
-
Volume 82 (1974)
-
Volume 81 (1974)
-
Volume 80 (1974)
-
Volume 79 (1973)
-
Volume 78 (1973)
-
Volume 77 (1973)
-
Volume 76 (1973)
-
Volume 75 (1973)
-
Volume 74 (1973)
-
Volume 73 (1972)
-
Volume 72 (1972)
-
Volume 71 (1972)
-
Volume 70 (1972)
-
Volume 69 (1971)
-
Volume 68 (1971)
-
Volume 67 (1971)
-
Volume 66 (1971)
-
Volume 65 (1971)
-
Volume 64 (1970)
-
Volume 63 (1970)
-
Volume 62 (1970)
-
Volume 61 (1970)
-
Volume 60 (1970)
-
Volume 59 (1969)
-
Volume 58 (1969)
-
Volume 57 (1969)
-
Volume 56 (1969)
-
Volume 55 (1969)
-
Volume 54 (1968)
-
Volume 53 (1968)
-
Volume 52 (1968)
-
Volume 51 (1968)
-
Volume 50 (1968)
-
Volume 49 (1967)
-
Volume 48 (1967)
-
Volume 47 (1967)
-
Volume 46 (1967)
-
Volume 45 (1966)
-
Volume 44 (1966)
-
Volume 43 (1966)
-
Volume 42 (1966)
-
Volume 41 (1965)
-
Volume 40 (1965)
-
Volume 39 (1965)
-
Volume 38 (1965)
-
Volume 37 (1964)
-
Volume 36 (1964)
-
Volume 35 (1964)
-
Volume 34 (1964)
-
Volume 33 (1963)
-
Volume 32 (1963)
-
Volume 31 (1963)
-
Volume 30 (1963)
-
Volume 29 (1962)
-
Volume 28 (1962)
-
Volume 27 (1962)
-
Volume 26 (1961)
-
Volume 25 (1961)
-
Volume 24 (1961)
-
Volume 23 (1960)
-
Volume 22 (1960)
-
Volume 21 (1959)
-
Volume 20 (1959)
-
Volume 19 (1958)
-
Volume 18 (1958)
-
Volume 17 (1957)
-
Volume 16 (1957)
-
Volume 15 (1956)
-
Volume 14 (1956)
-
Volume 13 (1955)
-
Volume 12 (1955)
-
Volume 11 (1954)
-
Volume 10 (1954)
-
Volume 9 (1953)
-
Volume 8 (1953)
-
Volume 7 (1952)
-
Volume 6 (1952)
-
Volume 5 (1951)
-
Volume 4 (1950)
-
Volume 3 (1949)
-
Volume 2 (1948)
-
Volume 1 (1947)